A magnetic body of a double structure having a core part and a shell part is subjected to a solid solution treatment, a wire drawing process and a heat treatment which are repeatedly performed, and a twisting process to form a combined magnetic wire. The combined magnetic wire is known as exhibiting the so-called large Barkhausen effect, a phenomenon in which magnetization reversal may occur all at once near the boundary of the south and north poles of a magnet. By detecting the magnetization reversal of a combined magnetic wire using a pickup coil, a constantly uniform power generation pulse can be obtained regardless of the rotation speed of an object under detection such as a motor. Therefore, the combined magnetic wire is widely used in rotation detection device.
As a rotation number detector by self-power generation using a combined magnetic wire and a pickup coil, techniques are disclosed in Patent Literatures 1 to 3. A rotation number detector in Patent Literature 1 discloses a technique in which a magnet magnetized with a south pole and a north pole, and a power generation device of a combination of a combined magnetic wire having the large Barkhausen effect and a pickup coil are used to back up the power of the detector by power supply from the power generation device. In the power generation device, two power generation elements whose phase difference is 90 degrees with respect to one rotation are disposed.
The rotation number detector in Patent Literature 2 discloses a technique in which an even number of elements of wire-wound magnetic wires are disposed radially around a magnet, and inductance variations in the elements along with displacement of the magnet in a vertical direction are converted into electric signals.
The rotation number detector in Patent Literature 3 discloses a technique in which a plurality of power generation elements having combined magnetic wires and pickup coils is disposed such that the combined magnetic wires cross on a rotation center to determine a rotational direction.